Fucoidan and alginate from brown seaweeds: extraction, structural diversity, biocompatibility, biodegradability, and biomedical applications.

Brown seaweeds are among the richest marine sources of structurally diverse polysaccharides, especially fucoidan and alginate, which have attracted significant attention as multifunctional biomaterials for pharmaceutical, biomedical, and regenerative medicine applications. This review provides a comprehensive overview of extraction and purification methods, including conventional chemical, enzymatic, microwave-assisted, and ultrasound-assisted techniques, discussing how these methods affect yield, purity, molecular weight distribution, sulfation patterns, and structural integrity. An in-depth examination of the chemical structure of fucoidan and alginate highlights the importance of monosaccharide composition, sulfation degree, M/G ratio, molecular weight, and block arrangement in influencing bioactivity, gelation, biodegradability, and interactions with biological systems. The review thoroughly evaluates biocompatibility and biodegradation mechanisms, focusing on the roles of impurities, crosslinking density, oxidation levels, enzymatic degradation pathways, and environmental factors. It also summarizes recent advances in fucoidan- and alginate-based formulations, including hydrogels, nanoparticles, films, nanofibers, microspheres, sponges, injectable gels, and composite scaffolds, as well as key drug delivery mechanisms like ionotropic gelation, diffusion-controlled release, pH-responsiveness, mucoadhesion, and stimuli-responsive behaviors. By combining structural insights with emerging biomedical applications, this review highlights the remarkable versatility of fucoidan and alginate as next-generation marine biomaterials and explores their expanding potential in drug delivery, tissue engineering, wound healing, and multifunctional therapeutic systems.